Parasitoid insects and natural predators of agricultural pests have become the best allies to combat them. The techniques of biological control of pests are consolidated as an alternative to the chemical respectful of our environment to eliminate these harmful insects.
In a society that values more profitability in food production than their quality or appearance and uniformity than smell and taste, more and more people say enough is enough. People who want their tomatoes to taste like tomatoes and who are not willing to use pesticides with oil and salt as a condiment in their salads. We can say that in Europe we are living a return to the origins, a true green boom, where ecological and sustainable agriculture has gained special importance.
One of the fundamental pillars in this type of agriculture is the biological control of pests, that is, the use of natural enemies (usually other insects, but also fungi, bacteria, and other invertebrates) to control the pest species, since so that a crop can be labeled as organic should not contain even the slightest trace of pesticides.
What is known as a plague?
The word plague comes from Latin and means damage or injury. Initially, there was talk of the massive and sudden appearance of living beings of the same species that cause serious damage to animal or plant populations (RAE, 2001). This basically includes any living organism causing damage or disease to man or his possessions, however, this definition entails striking paradoxes, such as the fact that in this case humanity itself should be considered as a plague.
Today, the concept of plague is accepted to refer exclusively to the damage caused by animals, compared to the concept of disease, which refers to the damage caused by other biotic agents. What seems clear is that the concept of plague has an unequivocal anthropocentric component. That is, we will consider as pests those species that bother us, either because they produce economic losses or cause health problems.
For example, termites. From a formal point of view, they should be considered a useful insect, since they return the remains of wood from dead trees in the forests to the earth cycle, and yet they are one of the most feared and fought pests worldwide. Why? Because nobody imagined that a primate with pretensions was going to start building their houses with dead trees!
Pest Control Methods
But seriously, there are currently many techniques for pest control, since the most classic and traditional ones have to be added those derived from the biotechnological revolution of the last 20 years. Broadly speaking, we can classify them into three main groups: chemical control,
biological control, and part biological control. While the so-called Biological Control is based on the direct and directed manipulation of natural enemies and competitors of the pest species, or of the resources required by these organisms, the Parabiological Control refers to the direct and directed manipulation of the pest species themselves, or of its resources.
Basically, in the biological control, predatory or parasitoid insects that interact with the pest species are used to reduce their population, and in the part, biological control from traditional cultural techniques such as crop rotation to the use of new technologies such as ionizing radiation to create males sterile These are released in large quantities in the natural environment, so that they compete with the fertile males in the access to the females and if they manage to cross they will not give offspring.
The Biological Control
It consists of manipulating the ecosystem so that we can reduce the population of the species to a density that does not produce significant damage. To do this, we must first consider where the limit of damage is from which, we can no longer consider the population level acceptable. It is what is called the tolerance threshold, which will obviously be very variable depending on the specific circumstances of each pest.
Once this limit is established, the natural enemy of the pest species suitable for each case must be located. For this, it is important to look at 5 basic characteristics: 1) its specificity with respect to the species to be controlled, 2) synchronization with the pest rhythm, 3) that it develops rapidly, 4) that it is able to survive without food and 5 ) that is effective locating the plague.
Within the methods of biological control of pests, we can choose between three groups of natural enemies. The use of predators such as mites, beetles, bed bugs and Hymenoptera. The use of parasitoids, insects whose larva feeds exclusively inside the pest insect that it ends up killing, especially highlighting several groups of Hymenoptera and some dipterans. And finally the application of pathogenic organisms, which encompasses the use of fungi, bacteria, viruses and also nematodes, which although they are really animals are grouped with this type of organism because their mechanism of action is very similar.
We can also use different strategies when using them. The introduction of an exotic natural enemy is the first of them and consists of locating a predator or parasitoid at the place of origin of the pest, and if possible, raising it and introducing it to be established. When we talk about exotic pests it is sometimes the only option, and it has given spectacular results, as in the case of the citrus grooved cochineal, Iceria purchase, which is controlled with the Rodolia cardinalis beetle in more than 20 countries.
But we can also increase the number of natural enemies of the plague. We will use this technique when for different reasons the population levels of your enemies are very low or non-existent. To obtain them, they are raised in mass and then controlled loose in the crop. The last strategy is to conserve native natural enemies by manipulating the habitat to increase effectiveness, for example by allowing the existence of harmless alternatives for cultivation that serves as food.
Case studies in Spain
The use of biological pest control techniques is deeply rooted in our territory. Both citrus crops throughout the east and in the greenhouses of Almeria have been used for a long time with great results.
In the case of citrus fruits, for example, we can find, among many others, three species of cochineal, each one of them fought with a different natural enemy: Ribbed cochineal is treated with a beetle, Rodolia cardinalis, cottony cochineal, Planococcus citri, with another beetle, Cryptolaemus montrouzieri . And the so-called California red louse, Aonidiella aurantii, with a parasitoid hymenopter, the aphelinid Aphytis melinus.
A variety of natural enemies are being used in horticultural crops in Almeria. We can highlight a genus of Neuropter called Chrysoperla, used with great success in controlling aphids in vegetable crops such as pepper, cucumber, celery, lettuce, strawberry, and eggplant. Several bed bug (Hemiptera) spices are also used, such as Orius laevigatus, which fights thrust pests, such as Frankliniella occidentalis and Trips tabaci, or Macrolophus melanotoma and Diciphus tamanini that fight several species but are especially important in the control of whiteflies, Trialeurodes vaporarium, and Bemisia tabaci.
And outside the agricultural interest, we could not fail to mention the most painful recent example, for what it represents for the Mediterranean plant heritage, the palm weevil plague, Rhynchophorus ferrugineus. A beetle native to Southeast Asia and which mainly affects the Canary Islands, Phoenix canariensis, and date palms, Phoenix dactylifera. In its control, along with other methods, an entomopathogenic nematode, Steinernema carpocapsae, is used. Despite the efforts, it is increasingly common to find cut palm trees in our landscape. Even so, the scientific community works to find a more effective solution according to the aggressiveness of this plague.